Star Sapphire is the name of several supervillainesses in DC Comics, all connected in origin. For millions of years, an immortal race of warrior women, the Zamarons, had chosen physically identical mortals from across the cosmos to serve as host body for their Queen, whom they called Star Sapphire. She is then given the Queen's symbolic weapon, a crystal resembling an actual star sapphire which grants the user powers similar to the power ring of a Green Lantern.
The first version of the character appeared during the Golden Age and battled the Flash twice.
The second Star Sapphire was Carol Ferris, girlfriend of Hal Jordan. She battled Jordan (as Green Lantern) for many years, and once Jordan became the Spectre he removed the Star Sapphire persona from Ferris.
A third woman became Star Sapphire during the same time as Carol Ferris.
During a charity event, Carol Ferris is mysteriously attacked. Green Lantern rescues her and takes her to the hospital. There, she awakens and seeks out the star sapphire jewel. When she finds it, she resumes her Star Sapphire identity. Green Lantern finds her, but she stuns him and leaves.
When Hal recovers, he follows Star Sapphire. He finds her battling another woman who is also Star Sapphire. The Zamarons meet GL and explain that the other woman is Dela Pharon from the planet Xanador. The Zamarons chose her as their new queen, but the woman became angry when dissenters claimed that Carol would have made a superior queen. Dela came to Earth and attacked Carol. This provoked Carol to become Star Sapphire again.
The two women finish their duel with Carol seemingly the victor. She then challenges and defeats GL, forcing him to return to Zamaron as her husband. Before the wedding, GL discovers that the woman is really Dela Pharon. She has tricked everyone in order to marry GL. Hal brings the real Carol, who was living Dela Pharon's life on Xanador, to Zamaron. He then defeats Dela and returns Carol to Earth with no knowledge of events or her Star Sapphire persona (Green Lantern v2 #41, Dec 1965).
Dela reappears in a story told by Carol Ferris. She continued as Star Sapphire, eventually enslaving the Green Lantern of Xanador, becoming his mate, killing him, and then encasing the planet in a crystal, suspended for the rest of time.
A new Star Sapphire is introduced in Green Lantern (vol. 4) #15. The gem first takes possession of a girl named Krystal, and then seeks out Carol Ferris. Ferris is released once the gem discovers that Hal Jordan bears affection for Jillian "Cowgirl" Pearlman.
Ferris reveals to Jordan that during the time the gem possessed her, she gained knowledge of the Star Sapphire: they come from Sector 1416 and comprise a Star Sapphire Corps whose purpose is to spread love throughout all 3600 sectors of the universe. The members of the Corps are Oans who, after migrating to Zamaron, found a parasitic crystal which they shaped into several Star Sapphires. These were used to empower females who had been loved and spurned, providing them the opportunity for revenge.
In the afterlude of this incident, the Zamarons are shown converting the Star Sapphire (which Hal Jordan had tricked into latching onto one of the Zamarons) into a power ring and lantern, which they place on a dais which contains a ring and lantern set of the Green Lantern Corps and the Sinestro Corps, alongside several ring/lantern sets of different colors mentioning that they must collect all emotions in order to combat "the Prophecy". They create their own Main Power Battery, and begin recruiting members for their Corps shortly after that. Their first recruit was Miri Riam of the planet Lartnec, who had just lost her husband to an attack by Mongul.
As with her powers, the limitations of the Star Sapphire are unclear. Psychologically, she has displayed a bizarre preoccupation with gender, suspected of reflecting a pathological fear of men. She also has a less than accurate grasp of the variations in physics between dimensions. She has been foiled in both of her recorded cases primarily by her own overconfidence.
Star Sapphire joined Lex Luthor's cause when he asked for villains to help him destroy the Justice League, she loses against Green Lantern in comical fashion (while they were fighting a large statue was flung at her back which Green Lantern proceed with "Duck!" She typically doesn't believe him and gets knocked out by a giant duck figurine to which Green Lantern remarks "I tried to warn her"). When that failed, she joined forces with Aresia to destroy the men of the world. She successfully tricked Wonder Woman and Hawkgirl into believing that she cared about the men, leading them into a trap that took them and Wonder Woman's mother, Hippolyta, on board of Aresia's plane. She was knocked out by Wonder Woman and she fell to the sea, but later she showed up again to battle Green Lantern, losing that battle as well. She was seen several times during the final season of Justice League Unlimited. She was part of Grodd/Luthor's Secret Society.
Star Sapphire's power comes from the stone in her mask, giving her Green Lantern-like power that enables her to form shields, create energy constructs, fire power blasts, and fly into orbit. Her origins are never elaborated upon, making it difficult to tell which version of Star Sapphire this is, though in appearance she seems to be based on the Carol Ferris version. Carol Ferris is an American in all other iterations, while the Justice League version clearly has an English accent.